7. analytical methods - agency for toxic … 259 7. analytical methods ... used as the standard...

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7. ANALYTICAL METHODS

The purpose of this chapter is to describe the analytical methods that are available for detecting,

measuring, and/or monitoring xylene, its metabolites, and other biomarkers of exposure and effect to

xylene. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to

identify well-established methods that are used as the standard methods of analysis. Many of the

analytical methods used for environmental samples are the methods approved by federal agencies and

organizations such as EPA and the National Institute for Occupational Safety and Health (NIOSH). Other

methods presented in this chapter are those that are approved by groups such as the Association of

Official Analytical Chemists (AOAC) and the American Public Health Association (APHA).

Additionally, analytical methods are included that modify previously used methods to obtain lower

detection limits and/or to improve accuracy and precision.

The analytical methods used to quantify xylene in biological and environmental samples are summarized

below. Table 7-1 lists the applicable analytical methods used for determining xylene in biological fluids

and tissues. Table 7-2 lists the methods used for determining xylene in environmental samples.

7.1 BIOLOGICAL MATERIALS

Extensive commercial, industrial, and domestic use of volatile organic chemicals such as xylene virtually

assures that the general population will be exposed to this class of chemicals to some extent. The

determination of trace amounts of xylene in biological tissues and fluids has been restricted to only a

limited number of analytical methods. These include gas chromatography coupled with mass

spectrometry (GC/MS), gas chromatography coupled with hydrogen flame ionization detection (GC/FID),

and high-performance liquid chromatography (HPLC).

Xylene can be detected at parts-per-trillion (ppt) levels in whole human blood using a purge and trap

apparatus followed by GC/MS; however, this method does not distinguish between m- and p-xylene

(Ashley et al. 1992). Antifoam agents are frequently used, although a method has been developed that

does not require this additive (Cramer et al. 1988). The use of a dynamic headspace purge at room

temperature reduces the absolute recoveries of the late eluting compounds. An advantage of this GC/MS

technique is that it can be used in conjunction with selected ion monitoring to obtain better sensitivity of

target compounds (such as NPL Pollutants) at ppt levels (Cramer et al. 1988).

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Table 7-1. Analytical Methods for Determining Xylene in Biological Materials

Sample Analytical Sample Percent matrix Preparation method method detection limit recovery Reference Human Adsorb directly to Amberlite GC/FID No data 77B98 Norstrom blood XAD 2 resin; extract with (m-xylene) and

carbon disulfide Scheepers 1990

Human Purge and trap sample on GC/MS 1 ng/mL No data Cramer et blood Tenax TA trap (m-xylene) al. 1988 Human Purge and trap sample on GC/MS 5.2 ng/mL No data Antoine et blood sorbent al. 1986

0.019 ng/mL No data Ashley et al. (m-, p-xylene); 1992 0.035 ng/mL (o-xylene)

Tissues and Saturate sample with sodium GC/FID 0.05 mg/100 g No data Bellanca et body fluids chloride and seal in a vial; and (m-, p-xylene); al. 1982

inject into gas chromatograph GC/MS 0.01 mg/100 g (o-xylene)

Urine Derivatize or methylate GC/FID <0.25 g/L 110.7 (m-MHA) de Carvalho sample with HCl and et al. 1991 methanol; cool; extract with chloroform

Urine Extract sample with THA-OH; GC/FID 1 ng (o-, p-, 94.2 (o-MHA); Kataoka et alkylate with isopropyl m-MHA) 96.0 (m-MHA); al. 1991 bromide; wash with silver 97.6 (p-MHA) sulfate; dry; redissolve in ethyl acetate

Urine Adsorb to filter paper; extract HPLC 4 ng (o-MHA 99B99.9 Astier 1992 with methanol; dilute with and m-MHA) (o-MHA); mobile phase or water 97.2B99.9

(m-MHA) Urine Adsorb to Sep-Pack C18 HPLC 10 μg/mL 94.7B96.1 Tanaka et

cartridge; elute with methanol (xyl-m) (xyl-m) al. 1990 Urine Acidify with H2SO4; extract HPLC 0.1 μmol (o-, p-, 91 (o-MHA); Tardif et al.

with methyl-t-butyl ether; m-MHA) 107 (m-MHA); 1989 concentrate 113 (p-MHA)

Urine Acidify with HCl, saturate with HPLC/ UV 0.2 mg/mL 98 NIOSH 1994 sodium chloride; extract with (methyl hippuric (Method ethyl acetate; dry and acid; method 8301) redissolve in distilled water does not

distinguish between p- and m- isomers)

Urine Acidify sample and extract GC/FID 5 mg/L 81.5 (o-MHA); Caperos with ethyl acetate and 82.2 (m-MHA); and methylating solution 84.8 (p-MHA) Fernandez

1977

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Table 7-1. Analytical Methods for Determining Xylene in Biological Materials

Sample Analytical Sample Percent matrix Preparation method method detection limit recovery Reference Urine Adjust pH of sample to 2.0; GC/FID No data 98 (m-MHA) Engstrom et

extract with ethylacetate al. 1976 Urine Acidify sample with HCl and GC/FID No data 88.7B95 Morin et al.

extract with ethylacetate; add (m-MHA); 1981 methanol to ethylacetate 79.3B82 extract; methylate extract with (p-MHA) diazomethane in diethyl ether solution

Urine Acidify sample HPLC No data CV=4.8 Astier 1992 Urine Acidify sample with HCl; HPLC 0.1 mg/mL No data Poggi et al.

extract with n butyl (m-MHA) 1982 chloride:isopropanol (9:1)

Urine Adjust pH of sample to 2.0; HPLC 0.02 μg/sample No data Sugihara extract with methyl ethyl (m-MHA); and Ogata ketone; add phenacyl bromide 0.02 μg/sample 1978 solution to extract and heat (p-MHA)

Urine Add sample specimen to HPLC 6 mg/L (o-MHA); 102 (o-MHA); Ogata and methanol; centrifuge 8 mg/L 102.4 (m-MHA); Taguchi

(m-MHA); 99.5 (p-MHA) 1987 8 mg/L (p-MHA)

Urine Acidify sample; extract with TLC 6 μg/mL 100 (m-MHA) Bieniek and chloroform and concentrate (m-MHA) Wilczok

1981 Exhaled Trap sample on charcoal GC/FID 0.06 ppm 90 Glaser and breath cloth; desorb with carbon (m-xylene) Arnold 1989;

disulfide Glaser et al. 1990

Exhaled Sorb to Tenax TA tube; GC/FID 0.03 ppm 60 (m-xylene) Glaser et al. breath thermally purge 1990 Exhaled Sorb to Tenax GC tube; dry; GC/MS 0.50 μg/m3 No data Pellizzari et breath thermally desorb al. 1988 Whole body Kill mice and inject with GC/FID No data 86 (m-xylene) Tsuruta and (mice) solvent sample; homogenize Iwasaki

sample in liquid nitrogen; 1984 evaporate liquid nitrogen and extract with carbon disulfide

Fish Freeze sample; homogenize GC/MS No data No data Hiatt 1983 in liquid nitrogen; vacuum equipped distillation with fused-

silica capillary column

CV = coefficient of variation; GC/FID = gas chromatography/flame ionization detector; GC/MS = gas chromatography/mass spectrometry; HCl = hydrochloric acid; HPLC = high performance liquid chromatography; H2SO4 = sulfuric acid; MHA = methylhippuric acid; THA-OH = tetrahexyl ammonium hydroxide; TLC = thin-layer chromatography; UV = ultra violet; xyl-m = N acetyl-s-xylyl-L-cysteine

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Table 7-2. Analytical Methods for Determining Xylene in Environmental Samples

Sample Analytical Sample matrix Preparation method method detection limit Percent recovery Reference Air Collect sample on porous GC/FID 0.1 ppm No data Brown 1988b

polymer adsorbent; thermally desorb

Air Sorption to a tube GC/MS 4.0 ng/tube 93B103 (o-xylene); Chan et al. containing Tenax, (5B50-L air 90.8 (p-, m-xylene) 1990 Ambersorb XE 340, and sample) charcoal; thermally desorb

Air Draw sample through GC/PID 0.3 ppb No data Hester and copper tubing with a Meyer 1979 diaphragm pump

Air Absorption on Tenax GC GC/MS No data No data Hampton et al. air sampler 1982

Air Collect on coconut shell GC/FID 2.6 mg No data NIOSH 1994 charcoal personal sampler; (Method 1501) desorb with carbon disulfide

Air Pump air sample through GC/FID <0.05 ppm 51B86 (o-xylene); Brown 1988a; charcoal tubes; extract (o-xylene); 51B86 (p-xylene) Otson et al. charcoal with carbon <0.05 ppm 1983 disulfide (p-xylene)

Air Collect sample in Tedlar GC/FID No data No data Lonneman et bags by means of an al. 1974 automated sequential large air sampler

Air Collect air on activated GC/FID 1 μg/μL 92B100 Esposito and charcoal; desorb with carbon disulfide; shake with

LC/UV No data 92B104 Jacobs 1977

75% H2SO4

Air Collect sample in GC 1.3 pg/sample No data Nutmagul et al. pressurized stainless steel FID/PID (o-xylene) 1983 cannister

Air Collect sample in a GC <1 ppm No data Pleil et al. 1988 pressurized cannister FID/ELCD

and GC/MS

Air Collect sample on silica GC No data >99% Whitman and gel; extract with isopropyl Johnston 1964 benzene

Drinking Purge and trap on sorbent GC/FID <1 μg/L 75 (o-xylene); 87 Otson and water (o-xylene); (m-xylene) Williams 1982

<1 μg/L (m-xylene)

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Sample Analytical Sample matrix Preparation method method detection limit Percent recovery Reference Drinking Extract sample in hexane GC/FID 2 μg/L 80B96 (o-xylene); Otson and water (o-xylene); 80B83 (m-xylene); Williams 1981

2 μg/L 78B85 (p-xylene) (m-xylene); 2 μg/L (p-xylene)

Water Purge and trap; methyl- GC/MS 0.06 μg/L 94 (o-xylene); NEMI 2005 silicone-coated packing is (o-xylene); 94 (m-xylene); (EPA Method recommended; desorb 0.03 μg/L 97 (p-xylene) 524.2) thermally (m-xylene);

0.06 μg/L (p-xylene)

Water Purge and trap; desorb GC/MS 0.24 μg/L 94 (o-xylene) NEMI 2005 thermally (o-xylene); 100 (m-xylene) (ASTM D5790)

0.48 μg/L 100 (p-xylene) (m-xylene); 0.48 μg/L (p-xylene)

Water Purge and trap; desorb GC/MS 0.03 μg/L 106 (o-xylene) NEMI 2005 thermally (o-xylene) (Standard

Methods 6200B)

Water Purge and trap; desorb GC/ELCD 0.02 μg/L 68 (o-xylene) NEMI 2005 thermally (o-xylene) (Standard

Methods 6200C)

Ground- Solid-phase microextration GC/FID 1 μg/L No data Arthur et al. water (methyl-silicone fiber 1992

coated with methyl-silicone film)

Water Purge and trap; methyl- GC 0.01B0.05 μg/L 90 (o-xylene) APHA 1992 silicone-coated packing is PC/PID 90 (m-xylene) (equivalent to recommended; desorb 85 (p-xylene) EPA Method thermally 503.1)

Water Purge and trap; methyl- GC 0.02 μg/L 99 (o-xylene) NEMI 2005 silicone-coated packing is CC/PID (o-xylene); 100 (m-xylene) (EPA Method recommended; desorb 0.01 μg/L 99 (p-xylene) 502.2) thermally (m-xylene);

0.01 μg/L (p-xylene)

Soil Extract sample with GC No data No data Anderson et al. methanol; centrifuge 1991

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Sample matrix Preparation method

Analytical method

Sample detection limit Percent recovery Reference

Sediment (clay)

Shake sample with water; purge and trap on Porapak N cartridges; elute with MeOH

GC ECD/PID GC/ELCD

7 ng/g; 1 ng/g

70B77 (p-xylene); 68B79 (o-xylene) No data

Amin and Narang 1985

Various Direct injection, purge and trap, or vacuum distillation

GC/PID 0.02 μg/L (o-xylene); 0.01 μg/L (m-xylene); 0.01 μg/L (p-xylene)

99 (o-xylene) 100 (m-xylene) 99 (p-xylene)

NEMI 2005 (EPA Method 8021B)

Various Direct injection, purge and trap, or vacuum distillation

GC/ELCD No data No data NEMI 2005 (EPA Method 8021B)

Various Purge and trap, azeotropic distillation, vacuum distillation, head space, or direct injection

GC/MS NA 106 (o-xylene) 106 (m-xylene) 97 (p-xylene)

NEMI 2005 (EPA Method 8260B)

Waste Extract waste with hexane GC/MS No data No data Austern et al. 1975

Waste Add sample to a small volume of ethanol and

GC/FID No data No data Austern et al. 1975

dilute with water or raw wastewater; adjust the pH; extract with Freon-TF

CC = capillary column; ELCD = electron capture detector; FID = flame ionization detector; GC = gas chromatography; H2SO4 = sulfuric acid; MeOH = methanol; MS = mass spectrometry; LC = liquid chromatography; PC = packed column; PID = photoionization detector; UV = ultraviolet spectrometry

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To overcome the low recoveries obtained with the purge and trap method, another extraction procedure is

recommended that uses Amberlite XAD-2 adsorbent resin present in the blood collection tube when the

sampling takes place. This method dispenses with the readsorption of the hydrocarbon from the sampling

tube to the polymer and gives recoveries of 77–98% (Norstrom and Scheepers 1990).

The use of GC/FID followed by a combination of packed and open tubular capillary GC and GC/MS to

detect and quantify the isomers of xylene in human tissues and fluids has been reported in the literature.

Brain, liver, lung, kidney, and blood samples of individuals who died following occupational exposure to

several organic solvents were analyzed using a combination of capillary columns (Bellanca et al. 1982).

The sensitivity and resolution of the isomers of xylene were increased, and detection limits of 0.05 mg,

0.05 mg, and 0.01 mg per 100 grams of sample were obtained for m-, o-, and p-xylene, respectively

(Bellanca et al. 1982). Despite this increased resolving power, adequate separation of m- and p-xylene

was unattainable.

Exposure to xylene may also be indicated by its presence in exhaled breath. Xylene in mainstream breath

may be determined by exhaling through a charcoal cloth (Glaser and Arnold 1989); xylene in sidestream

breath is trapped using a two-stage Tenax TA sorbent sampler (Glaser et al. 1990) or a Tenax GC

cartridge (Pellizzari et al. 1988). The Tenax cartridge is dried over calcium sulfate, and then the xylene is

thermally desorbed for GC/MS. Correlations with carbon dioxide measurements were 90 and 60% for

mainstream and sidestream breath, respectively (Glaser et al. 1990), with a quantification limit of

400 μg/m3 of m-xylene for a 50-L sample (Glaser and Arnold 1989). The detection limit (LOD) was

0.50 μg/m3 with a quantification limit 5 times the LOD for a 15-L breath sample (Pellizzari et al. 1988).

In addition to direct measurement of xylene in biological tissues and fluids, it is also possible to

determine the concentration of its metabolites in biological fluids. A simple, sensitive, and specific

automated HPLC technique was developed for direct and simultaneous quantification of o-, m-, and

p-methylhippuric acids, the metabolites of o-, m-, and p-xylene, respectively (Ogata and Taguchi 1987;

Sugihara and Ogata 1978; Tardif et al. 1989). A possible disadvantage of the HPLC technique is that at

low concentrations (<0.6 mg/L) in urine, these methylhippuric acids may not be distinguishable from

similar compounds. However, addition of a mobile phase, consisting of mixture of acetonitrile and 1%

phosphoric acid, has been used to distinguish between xylene metabolites and other solvents such as

benzene and toluene in the urine (Astier 1992). Use of methanol as a solvent for the urine obviates the

need for the customary ethylether extraction step and allows direct urine injection for HPLC (Ogata and

Taguchi 1988). N-Acetyl-S-xylyl-L-cysteine, a mercapturic acid, is also a urinary metabolite of xylene

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that may be detected by direct HPLC (Tanaka et al. 1990). The HPLC method recommended by NIOSH

(1994) does not distinguish between p- and m-methylhippuric acids.

Other techniques that have been successful in quantitatively determining urinary concentrations of

metabolites of xylene include GC/FID, GC/MS, and thin layer chromatography (TLC). GC/FID and

GC/MS offer the possibility of excellent analytical sensitivity and specificity for urinary metabolites of

xylene (Caperos and Fernandez 1977; de Carvalho et al. 1991; Engstrom et al. 1976; Kataoka et al. 1991;

Kira 1977; Morin et al. 1981; Poggi et al. 1982). However, most GC analytical methods require the

urinary metabolites to be chemically transformed into methyl esters or trimethyl silyl derivatives using

ethylacetate or diazomethane. This transformation, however, is problematic and may subsequently cause

low reproducibility (Caperos and Fernandez 1977; Engstrom et al. 1976; Morin et al. 1981; Poggi et al.

1982). The methylhippuric acid metabolites of the xylene isomers may be distinguished using an

extractive alkylation procedure followed by capillary GC analysis (Kataoka et al. 1991). An extraction

method using less toxic reagents (hydrochloric acid with methanol) has been developed (de Carvalho et

al. 1991).

A simple and highly reproducible TLC method has been developed for the detection and separation of m-

or p-methylhippuric acid in the urine of individuals exposed to a mixture of volatile organic solvents

(Bieniek and Wilczok 1981). However, the authors noted that this analytical technique is time

consuming. Furthermore, the developing agent used in this technique (p-dimethylamine benzaldehyde in

acetic acid) has the disadvantage that it is irritating to the eyes and mucous membranes. The sensitivity of

this method was reported to be 6 μg hippuric acid per 1 mL urine with a recovery of 100%.

When measuring hippuric acids in the urine of workers exposed to xylenes, NIOSH (1994) recommends

that a complete spot voiding sample be collected at the end of the shift after 2 days of exposure. As a

preservative, a few crystals of thymol should be added to the sample. It should be stored at 4 °C if

analysis is within 1 week. The sample should remain stable for 2 months if it is stored at -20 °C.

7.2 ENVIRONMENTAL SAMPLES

A gas chromatograph equipped with an appropriate detector is the basic analytical instrument used for

determining environmental levels of xylene. Precautions in the isolation, collection, and storage of

xylene in environmental media are necessary to prevent loss of the volatile xylene compounds to the air.

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The most common method for detecting aromatic hydrocarbons in air is the adsorption of the vapors to

either activated charcoal with extraction using carbon disulfide or adsorption to a polymer adsorbent, such

as Tenax GC, with thermal desorption. Each method is then followed by injection of the desorbed sample

into a gas chromatograph equipped with FID (Brown 1988a, 1988b; NIOSH 1994). The activated

charcoal method requires a 12-L air sample, while the polymer adsorbent uses a smaller 5-L sample for

determination of the xylene in the sub-parts-per-million range. A GC/MS method has also been

developed which uses an adsorbent tube with layers of Tenax, Amberlite, and charcoal (Chan et al. 1990).

The use of a molecular sieve to remove water vapor prior to adsorption has been recommended to

increase recovery of the hydrocarbons (Whitman and Johnston 1964). A computer-controlled, high-speed

GC system has been developed for rapid analysis of volatiles in air (and other media with appropriate

vapor generation). The system combines an electrically heated cold-trap inlet (with a vacuum

backflushing device on the GC) with a conventional FID. The advantage of the system is that a complete

analysis cycle requires only 10 seconds to detect p-xylene at a level of 13.4 ppb (Rankin and Sacks 1991).

A differential optical absorption spectrophotometer has also been used to monitor o-xylene in air; this

method gives a correlation coefficient of approximately 0.66 when compared with standard GC methods

(EPA 1991a).

An automated gas chromatograph with photoionization detector (GC/PID) has been developed by Hester

and Meyer (1979) to identify gas-phase hydrocarbons (including xylene) for complex systems such as

vehicle exhaust gas. The GC/PID method allows for measurement of sub-parts-per-billion level

concentrations of air contaminants and does not require trapping or freeze-concentration of samples

before analysis. These latter preconcentration steps are usually necessary because of the limited

sensitivity of FID techniques commonly used in the analysis of environmental samples. A limitation of

the GC/PID technique is that m- and p-xylene are detected but not well separated. GC/PID in tandem

with FID was used to obtain a more sensitive method to determine xylene levels in the air. A detection

limit of 1.3x10-12 g of o-xylene per sample was achieved (Nutmagul et al. 1983).

A purge and trap gas chromatographic method involving photoionization detection has been developed by

EPA to analyze volatiles in water (APHA 1992; NEMI 2005). A confirmatory analysis by a second

analytical column or by GC/MS is advised by EPA. The purge and trap gas chromatographic method can

detect the isomers of xylene and has a detection limit for o-, m-, and p-xylene of 0.2 ppb (Otson and

Williams 1981, 1982; Saunders et al. 1975). A purge and trap method using GC/MS has also been used

to detect xylene in waste water (Koe and Tan 1990).

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Emissions of volatile organic compounds from surface waters, including ponds at hazardous waste

treatment facilities, may be directly measured by the use of enclosure methods (such as a flux chamber or

surface impoundment simulator connected to collection canisters) followed by GC with the effluent split

between FID and an electron capture detector. Emission rates of 0.5 mg/minute/m2 could be measured

using the surface impoundment simulator with a precision of 3% relative standard deviation (Gholson et

al. 1991).

GC using both electron capture detection (ECD) and PID has been employed to determine xylene levels

in sediment samples (Amin and Narang 1985). The authors indicated that their method involved transfer

of samples between containers, and a considerable loss of volatile compounds was obtained.

A procedure has been developed to characterize volatile xylene compounds from fish samples by GC/MS

using a fused-silica capillary column (FSCC) and vacuum distillation (Hiatt 1983). The FSCC provides a

more attractive approach than packed columns for chromatographic analysis of volatile aromatic organic

compounds. An FSCC can be heated to a higher temperature (350 °C) than that recommended for packed

column, thereby improving the resolution (in ppb levels) of compounds and reducing column retention

times. A physical limitation for compounds that can be detected, however, is that the vapor pressure of

the compound must be >0.78 torr (≈50 °C) in the sample chamber (Hiatt 1983).

7.3 ADEQUACY OF THE DATABASE

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether

adequate information on the health effects of xylene is available. Where adequate information is not

available, ATSDR, in conjunction with NTP, is required to assure the initiation of a program of research

designed to determine the health effects (and techniques for developing methods to determine such health

effects) of xylene.

The following categories of possible data needs have been identified by a joint team of scientists from

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean

that all data needs discussed in this section must be filled. In the future, the identified data needs will be

evaluated and prioritized, and a substance-specific research agenda will be proposed.

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7.3.1 Identification of Data Needs

Methods for Determining Biomarkers of Exposure and Effect.

Exposure. The methods for determining xylene levels in blood and tissue samples and exhaled breath,

GC/MS or GC/FID, have sufficient sensitivity to measure xylene levels associated with background

levels of exposure as well as xylene levels at which biological effects occur. GC/MS has been employed

to detect o-xylene at ppm levels in the blood (Ashley et al. 1992; Cramer et al. 1988). However,

development of a GC/MS method that incorporates a less rigorously heated purge would be useful.

Heated purges currently used in GC/MS have the disadvantage of reducing the absolute recoveries of

volatile organic solvents. Better resolution and sensitivity are achievable with the application of a

capillary GC/MS column and selection of an appropriate detector or detector combination as an

alternative to the packed column approach currently in use. Also, there is a growing need for analytical

methods to efficiently separate and quantify trace levels of the isomers of xylene in biological media.

Analytical methods are also available to detect and quantify the xylene metabolites present in the urine

which have been correlated with exposure levels (Kawai et al. 1991; Ogata et al. 1979). These methods,

HPLC (Astier 1992) and GC (coupled with MS or FID) (de Carvalho et al. 1991; Kataoka et al. 1991;

Poggi et al. 1982), have been well characterized with respect to their precision, accuracy, reliability, and

specificity and have sufficient sensitivity to measure xylene metabolite levels associated with biological

effects. However, these methods may not be sensitive enough to measure metabolite levels associated

with background exposure levels.

Currently, no methods are available to quantitatively correlate monitored levels of xylene in tissues with

exposure levels or toxic effects in humans, although simultaneous measurement of xylene in exhaled

breath and ambient air may prove instrumental in indicating exposure, particularly in the workplace

(Glaser et al. 1990). These methods would provide the ability to evaluate possible health effects in

humans resulting from exposure to xylene.

Effect. No specific biomarkers of effect have been clearly associated with xylene exposure. Some

biological parameters such as hepatic microsomal enzyme activities and central nervous system activity

have been tentatively linked with xylene exposure. However, insufficient data exist to adequately assess

the analytical methods associated with measurement of these potential biomarkers.

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Methods for Determining Parent Compounds and Degradation Products in Environmental Media. Methods for determining xylene and its degradation products in environmental media would

help to identify contaminated areas and to determine whether the levels at contaminated sites constitute a

concern for human health. Standardized methods are available to detect xylene in air (Brown 1988a,

1988b; Chan et al. 1990; Rankin and Sacks 1991), waste water (Koe and Tan 1990), drinking water

(Otson and Williams 1981, 1982), fish (Hiatt 1983), and clay sediments (Amin and Narang 1985). There

is growing need for simultaneously achieving lower (less than ppb) detection limits, separating the m- and

p-isomers of xylene, and obtaining an adequate sample recovery. Such methods would provide useful

information for assessing the biological effects of exposure to xylene and for delineating dose-response

relationships. A combination of capillary gas chromatography coupled to a multi-detector system,

nuclear magnetic resonance (NMR) spectroscopy, and infra-red (IR) spectroscopy would be useful to

accurately identify and measure the isomers of xylene in complex environmental systems.

7.3.2 Ongoing Studies

The Environmental Health Laboratory Sciences Division of the National Center for Environmental

Health, Centers for Disease Control and Prevention, is developing methods for the analysis of xylene and

other volatile organic compounds in blood. These methods use purge and trap methodology, high-

resolution gas chromatography, and magnetic sector mass spectrometry, which give detection limits in the

low parts per trillion (ppt) range.

No other ongoing studies concerning the identification of xylene in biological materials or environmental

samples were identified.

7. analytical methods - agency for toxic … 259 7. analytical methods ... used as the standard...

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